1. Field of the Invention
The present invention relates to an image forming apparatus for electrophotography/electrostatic recording color cameras, color printers, color facsimiles and the like, and more particularly, to a color image forming apparatus that uses a laser for writing.
2. Description of the Related Art
As one example of the above-described technology the invention disclosed in Japanese Laid-Open Patent Application No. 8-149241 is known. In this invention, which is aimed at making it easy to expand a system, an image forming apparatus and its peripheral equipment are connected to each other by a system controller universal bus.
That is, in the invention of Japanese Laid-Open Patent Application No. 8-149241, a system control unit equipped with a CPU is connected to a printer unit and a plurality of scanner units as well as an image memory unit by a universal bus, image data from the image processing terminal equipment from the printer unit and the scanner unit is stored in the image memory unit via the universal bus, and image formation carried out by processing image data from the image processing terminal equipment in response to a data request, so system expansion can be carried out easily by connecting image processing terminal equipment to the universal bus.
According to such conventional art, expanding a system composed of a printer controller plus a scanner plus an image forming apparatus requires only a printer controller universal bus as a data transmission path, making system expansion easy.
However, when for example data read from the scanner unit undergoes image processing and the image-processed data is then printed out, the data is once stored in the system bus image memory, returned to the image processor inside the scanner unit and then transferred to the image forming apparatus via the system bus. In such a case, the amount of traffic on the bus increases, reducing transfer efficiency and resulting in reduced printer performance.
Such a problem can be solved by for example by using the system bus as the interface between the printer controller and the image forming apparatus and between the printer controller and the scanner unit, and using a different interface between the scanner unit and the image forming apparatus. With this type of interface configuration, the image forming apparatus must be compatible with both interfaces and the lighting timing control of a laser diode (LD) of each color must also be made compatible with both interfaces.
Additionally, as an image forming apparatus that adjusts a sub-scanning regist up to the timing of an operation commencement signal from a regist sensor and an electrostatic latent image formation operation commencement and in which a succeeding operation commencement signal becomes active during electrostatic latent image formation, there is for example a so-called tandem-type color image forming apparatus in which the image formation units are aligned along a conveyer belt.
In such type of image forming apparatus, the tandem configuration comprises a circuit that takes image data from an image input apparatus and controls a timing between each color and a laser diode control board for each color. However, it is necessary to match the timing of the image input apparatus and the timing laser diode control boards of the individual colors.
Accordingly, such an image forming apparatus has two requirements:
(A) The sub-scanning write position is determined by the timing delay to the commencement of writing from the reference regist sensor. The timing of the data request to the image input apparatus and the timing of the commencement of the FGATE for the laser diode control board must be synchronized to a rotation of a polygon mirror.
(B) In order to achieve high-speed operation, a method of electrostatic latent image formation simultaneously over a plurality of lines using a plurality of laser diodes has come to be used. Additionally, there is such a thing as write resolution, and sometimes images are written using a resolution greater than that of the original image (for example a resolution of 1200 dpi as opposed to 600 dpi of the original image), so a magnification process sometimes is performed at the laser diode control boards.
However, making the circuit that takes image data from the image input apparatus and controls the timing between each color compatible with the variety of write laser diode control board configurations and operating modes described above increases the scale of the circuitry and complicates control, which is undesirable.
Additionally, conventionally, copiers, printers and the like are equipped with an image forming apparatus that performs cyclical line scans on a photosensitive surface that moves in a sub-scanning direction using a laser beam carrying image information. The image formation unit of the image forming apparatus is equipped with a laser diode control board that generates a write signal for driving a laser diode in response to image data to be written sent from the application board, and which generates write signal corresponding to various image data sent from different application boards, for example a printer controller, a copy application, a FAX application, and so forth.
However, even with the three types of applications used as examples above, resolution differs because of differences in function among the applications. For example, among printer controllers, resolutions of 1200, 600 and 300 dpi are standard, but among copier applications a resolution of 600 dpi is standard while among FAX applications resolution is not measured in terms of dpi but in terms of lines per mm. In short, image density is variegated. As a result, it is necessary that the laser diode control board of the image formation unit variably control a rotation speed of a polygon motor and the frequency with which the LD is lit. However, such adjustment is not easy, and complicates the process of carrying out accurate image formation for applications of so many different kinds.
A multiplication method that sets the write density of the image forming apparatus to a 1200 dpi that is a minimum multiple of the image density and that doubles the difference between the image density and the write density using a line memory is commonly in wide use. However, even employing such a method, the interface between the application board and image formation unit is not uniform and incompatibilities can arise, making accurate image formation difficult. Such difficulties are particularly pronounced in the formation of color images of the tandem type, in which it is necessary to adjust the write positions of each of the colors.
Accordingly, it is a general object of the present invention to provide an image forming apparatus in which the above-described drawbacks are eliminated.
Another and more specific object of the present invention is to provide an image forming apparatus in which drive timing control of a laser diode for accommodating different interfaces can be performed simply.
Another, further and more specific object of the present invention is to provide an image forming apparatus that uses a data transfer method that guarantees the above-described operation of (A) and that solves the above-described problem of (B).
Still another, further and more specific object of the present invention is to provide an image forming apparatus that provides superior application board expansion capabilities for producing image data to be written and that includes means for generating a laser write signal that can form an image of a quality suited to color image processing.
The above-described objects of the present invention are achieved by providing a color image forming apparatus for forming a color image on a storage medium using a laser beam generated from a laser generating means, the color image forming apparatus comprising:
a plurality of image data interfaces provided between the color image forming apparatus and a peripheral device;
image data interface conversion means for converting each of the image data interfaces into an image data interface for the laser generating means; and
a single control means for controlling a drive timing of the laser generating means,
the control means controlling the drive timing of the laser generating means for each one of a plurality of colors based on image data input from the image interface conversion means.
According to the above-described invention, by using a single control means for controlling the drive timing of the laser generating means for at least the plurality of colors, the laser generating means drive timing control means (which corresponds to the laser diode control boards that drive the laser diodes in the embodiments described below) can be simplified.
Additionally, the above-described objects of the present invention are also achieved by the color forming apparatus as described above, wherein at least one of the plurality of image data interfaces is a PCI interface.
According to the above-described invention, by using a universal interface for the image data interface the design burden relating to the image data interface can be lightened.
Additionally, the above-described objects of the present invention are also achieved by the color image forming apparatus as described above, wherein at least one of the plurality of image data interfaces is a parallel interface synchronized to a predetermined clock.
According to the above-described invention, by using a parallel interface that transfers data with high efficiency, overall data transfer efficiency can be improved.
Additionally, the above-described objects of the present invention are also achieved by the color image forming apparatus as described above, wherein an image data interface for a drive means for the laser generating means is a parallel interface synchronized to a predetermined clock.
According to the above-described invention, using a parallel interface as the image data interface for the drive means for the laser generating means improves performance, maintains printer performance even when data transfer rates are low and is resistant to radiated noise frequently generated when the data transmission path is lengthened.
Additionally, the above-described objects of the present invention are also achieved by the color image forming apparatus as described above, wherein the control means manages an image transfer from the plurality of image data interfaces.
According to the above-described invention, using the laser diode lighting timing control means to manage data transfer allows the color image forming apparatus buffer memory capacity to be reduced because means for originally storing the data does not perform this processing.
Additionally, the above-described objects of the present invention are also achieved by the color image forming apparatus as described above, wherein the control means controls the drive timing of the laser generating means of each one of the plurality of colors independently.
According to the above-described invention, setting the timing to the same reference clock outputs images in which there is no mispositioning between individual colors.
Additionally, the above-described objects of the present invention are also achieved by the color image forming apparatus as described above, wherein the control is carried out based on a scanning synchronization signal corresponding to each one of the plurality of colors.
According to the above-described invention, conducting control based on the scanning synchronization signal outputs images in which there is no mispositioning between individual colors.
Additionally, the above-described objects of the present invention are also achieved by an image forming apparatus for forming an image on a storage medium using a laser beam generated from a laser generating means, the color image forming apparatus comprising:
an adjustment component that adjusts a sub-scanning regist up to the timing of an operation commencement signal from a regist sensor and an electrostatic latent image formation operation commencement, such that a succeeding operation commencement signal becomes active during electrostatic latent image formation;
a scanning synchronization signal generating component;
an image effective interval signal generating component; and
a line data synchronization signal generating component that generates a line data synchronization signal synchronized to image data of each line at least during an interval in which the image effective interval signal is active,
the image forming apparatus using the scanning synchronization signal, the image effective interval signal and the line data synchronization signal to transfer data.
According to the above-described invention, data transfer can be carried out without affecting laser diode control board configuration or operating modes, and without increasing either the scale of the circuitry or the complexity of the control.
Additionally, the above-described objects of the present invention are also achieved by the image forming apparatus as described above, wherein an image delay in a sub-scanning direction is controlled based on the scanning synchronization signal.
According to the above-described invention, data transfer can be carried out without affecting laser diode control board configuration or operating modes, and without increasing either the scale of the circuitry or the complexity of the control.
Additionally, the above-described objects of the present invention are also achieved by the image forming apparatus as described above, wherein an image effective interval signal length is controlled based on the line data synchronization signal.
According to the above-described invention, data transfer can be carried out without affecting laser diode control board configuration or operating modes, and without increasing either the scale of the circuitry or the complexity of the control.
Additionally, the above-described objects of the present invention are also achieved by the image forming apparatus as described above, wherein the line data synchronization signal includes a pulse of identical timing with respect to the scanning synchronization signal.
According to the above-described invention, synchronizing the laser diode write operation and the data transfer simplifies laser diode control board control and can reduce the scale of the circuitry.
Additionally, the above-described objects of the present invention are also achieved by the image forming apparatus as described above, wherein the line data synchronization signal includes a pulse of different timing with respect to the scanning synchronization signal.
According to the above-described invention, more flexible data transfer methods can be achieved than is conventionally the case.
Additionally, the above-described objects of the present invention are also achieved by the image forming apparatus as described above, wherein the pulse timing is variable.
According to the above-described invention, it is possible to avoid a variety of restrictions on data transfer that exist for each type of operation.
Additionally, the above-described objects of the present invention are also achieved by the image forming apparatus as described above, wherein the line data synchronization signal includes a pulse having a timing that corresponds to a number of beams of a laser diode that forms an electrostatic latent image.
According to the above-described invention, transferring a plurality of lines at a time corresponding to a number of diode laser beams emitted within a polygon synchronization signal interval makes it possible to achieve high speed laser writing.
Additionally, the above-described objects of the present invention are also achieved by the image forming apparatus as described above, wherein the line data synchronization signal thins out a pulse according to a sub-scanning multiple.
According to the above-described invention, transfer density can be decreased according to a sub-scanning multiple, and further, according to a polygon synchronization signal, simplifying laser diode control board control and reducing the scale of the circuitry.
Additionally, the above-described objects of the present invention are also achieved by the image forming apparatus as described above, wherein the line data synchronization signal includes a pulse having a timing corresponding to a sub-scanning multiple and a number of beams of a laser diode that forms an electrostatic latent image.
According to the above-described invention, combining the laser diode beam number and sub-scanning multiple to produce complex data transfer increases design flexibility.
Additionally, the above-described objects of the present invention are also achieved by an image forming apparatus for forming an image on a storage medium using a laser beam generated from a laser generating means, the image forming apparatus comprising:
an image forming component that includes means for periodically line scanning in a scanning direction a photosensitive body movable in a sub-scanning direction with a laser beam carrying image data and exposing a photosensitive surface using the laser beam;
an application board that produces image data and transfers the image data so produced to the image forming component;
trigger signal generating means for generating a scanning line trigger signal and a sub-scanning effective region trigger signal for transferring at a predetermined timing the image data from the application board to the image forming component based on a laser beam scan synchronization signal;
communication means for communicating the scanning line trigger signal and the sub-scanning effective region trigger signal to the application board; and
transferring means for generating a scanning line synchronization signal based on the communicated scanning line trigger signal and generating a sub-scanning effective region signal based on the sub-scanning effective region trigger signal, and transferring image data to the image forming component in synchrony with the scanning line synchronization signal and the sub-scanning effective region signal.
According to the above-described invention, images can be formed without having to include various data processing means in the image forming component (the laser diode control board) for correcting the laser diode exposure light position for each color in the case of a color image, combining image data and the like as is conventionally the case. Instead, such image processing means can be included in the application board (for example, the printer controller, copier application, facsimile application and the like) and the image data transfer timing generated from the image forming component. As a result, application board image memory can be effectively utilized, system-wide costs can be reduced, ease of application board expansion enhanced and images of high quality with no color blurring can be achieved.
Additionally, the above-described objects of the present invention are also achieved by the image forming apparatus as described above, wherein the transfer trigger signal generating means changes a period of a scanning line trigger signal to be produced according to a resolution of an image data produced by an application board.
According to the above-described invention, even when image data resolutions differ the laser diode write density can be fixed and image data can be produced that multiplies the scanning and sub-scanning resolutions at the laser diode control boards, and accordingly, write unit control can be simplified, permitting use of a simple interface that transfers image data at a rate of one line of image data for one scanning line synchronization signal.
Additionally, the above-described objects of the present invention are also achieved by the image forming apparatus as described above, wherein the transfer trigger signal generating means uses the interval in which the period of the scanning line trigger signal to be produced is changed as a period indicating an effective region of a sub-scanning effective region signal from the application board.
According to the above-described invention, the resolution and write density are only combined when the frame gate signal XIPUFGT output from the application boards is active, so the next print job can be quickly accommodated even when such job is generated quickly.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.